5] EVOLUTIONARY DEVELOPMENT AND PAST HISTORY 131 



mm ^JHHk 



Fig. 29. — Some primitive plant fossils. A, CoUenia iindosa, a Proterozoic fossil 

 believed to have been formed by the action of one or more Blue-green Algae 

 (after Walcott) ( < i); B, Nezvlondia concevtrica, a Proterozoic fossil apparently 

 formed by the action of a Blue-green Alga (after Walcott) ( < f); C, a Proterozoic 

 fossil, apparently a colonial Blue-green Alga consisting of aggregations of filaments 

 in globose sheaths (courtesy of E. S. Barghoorn and Science) ( ■ about 200); D, 

 a Proterozoic fossil of fungal or possibly algal type, showing spores and non- 

 septate hyphae (courtesy of E. S. Barghoorn and Science) ( • about 400); E, a 

 Cambrian Alga, Dalyia racemata (after Walcott) ( : about 3); F, a Cambrian 

 Alga, Morpolia aequalis (after Walcott) ( X about 2). 



